Surface feel (surface mobility) and surface smoothness and/or cushiness are attributes that consumers desire in their sanitary tissue products, for example bath tissue products. However, there has been a surface feel and/or surface smoothness and/or cushiness dichotomy. Historically when the surface feel and/or surface smoothness of a sanitary tissue product, such as bath tissue product, have been increased, the cushiness of the sanitary tissue product has decreased and vice versa. A technical measure of surface feel is average TS7 Emtec values of the sanitary tissue product, which is measured by the Emtec Test Method described herein. A technical measure of surface smoothness is slip stick coefficient of friction values of the sanitary tissue product, which is measured by the Slip Stick Coefficient of Friction Test Method described herein. A technical measure of cushiness is compressibility values of the sanitary tissue product which is measured by the Stack Compressibility and Resilient Bulk Test Method described herein. Current sanitary tissue products fall short of consumers' expectations for surface feel and surface smoothness and cushiness, with and more importantly without surface softening agents.
Emtec TS7 values, as outlined in the Emtec Paper Testing Technology user manual, are “dependent on the softness/hardness of the fibers (stiffness of the individual fibers) and structure of the material (bulk, binding of the fibers). The height of this peak TS7 correlates with the real material softness”. “Excitation of horizontal vibrations of the blades itself (in resonance frequency at approximately 6,500 Hz), caused by momentary blocking and swinging back of the blades by the fibers when moving over the surface.” In order to achieve low average Emtec TS7 values as measured according to the Emtec Test Method described herein and thus good surface mobility/real material softness, it has in the past been necessary for the sanitary tissue product to exhibit low Slipstick Coefficient of Friction values as well.
It is also desired for the sanitary tissue product to have a high level of compressibility to give the consumer the “cushiness” that is desired. Historically, as compressibility is increased, surface mobility (as represented by average Emtec TS7 values) becomes worse, thus resulting in higher average TS7 values as measured according to the Emtec Test Method described herein.
Formulators in the past believed that a creped surface of a fibrous structure, such as by creping the fibrous structure off a dryer or Yankee and/or by other means of foreshortening the fibrous structure, such as rush transfer steps in making the fibrous structure, was needed to achieve improved softness of fibrous structure and to achieve low average TS7 values. Such formulators have tried to utilize the EMTEC Tissue Softness Analyzer from Emtec Electronic GmbH of Leipzig, Germany to measure the softness (TS7) of creped fibrous structures and/or surface smoothness (TS750) of the creped surfaces of the sanitary tissue products. In the past, the formulators of sanitary tissue products apparently believed that creped surfaces of wood pulp fiber-containing fibrous structures were needed in order to attempt to measure softness of the creped fibrous structures using the EMTEC Tissue Softness Analyzer. It has been unexpectedly found that uncreped surfaces of fibrous structures can be measured using the EMTEC Tissue Softness Analyzer to measure softness of such fibrous structures, which is contrary to the teachings of the past.
Another problem with the past formulators' measurements using the EMTEC Tissue Softness Analyzer is that the measurements are very dependent upon which of two calibration methods is used in calibrating the EMTEC Tissue Softness Analyzer. Apparently, the past formulators failed to appreciate this fact and didn't indicate which of the two calibration methods were used or even if the EMTEC Tissue Softness Analyzer was calibrated at all. As a result the values the past formulators reported for TS7 and TS750 and other EMTEC Tissue Softness Analyzer values obtained from the EMTEC Tissue Softness Analyzer on creped surfaces of wood pulp fiber-containing fibrous structures are suspect at best, if not worthless from an absolute value point of view. At most, the values obtained by past formulators for creped fibrous structures may have value internally to the formulator from a relative perspective to show which versions of the same creped surface, wood pulp-containing fibrous structures differ in softness.
Accordingly, one problem faced by sanitary tissue product manufacturers is how to improve (i.e., decrease) the average TS7 Emtec values and/or the slip stick coefficient of friction properties, with and more importantly without surface softening agents, and improve (i.e., increase) the compressibility of sanitary tissue products, for example bath tissue products, to make such sanitary tissue products smoother and cushier to better meet consumers' expectations for more clothlike, luxurious, and plush sanitary tissue products since the actions historically used to make a sanitary tissue product smoother negatively impact the cushiness of the sanitary tissue product and vice versa.
Accordingly, there exists a need for sanitary tissue products, for example bath tissue products, that exhibit improved average TS7 Emtec values and slip stick coefficient of friction properties and improved compressibility properties, to provide consumers with sanitary tissue products that fulfill their desires and expectations for more comfortable and/or luxurious sanitary tissue products, and methods for making such sanitary tissue products.